The conventional way in the prevention of agricultural pests always involves the use of large amounts of chemical pesticides. However, long term usage of chemical pesticides may cause pests to attain resistance to the pesticides. Large dosages of pesticides also cause the problems of residuals of pesticides which could cause pesticidal pollution to the environment. Since chemical pesticides are potentially dangerous to human beings and the environment, the amounts of chemical pesticides should preferably be reduced whenever practicable and their applications limited. It is also preferred that the biocides to be used can effectively and selectively kill pests and which can be degraded in the environment. The quantity and types of biocides should be judiciously selected so that they will not harm human beings or crops.
One of the disadvantages of biocides is that most biocides cannot resist high temperatures. Preparations of biocidal formulation at high temperature may destroy biocides or reduce the activity thereof. Therefore, conventionally, the preparation of biocidal formulation must be processed at low temperature in order to protect biocides and maintain their activities.
R. L. Dunkle et at discloses a method for the preparation of starch-encapsulated Bacillus thuringiensis in Environment Entomology (vol. 17, 120-126, 1988). This reference teaches the preparation of starch-encapsulated biocide as follows. Refined corn oil (2 g) was mixed with pre-gelatinized starch powder (25 g), Chilled distilled water (60 ml, 2.degree. C.) containing a suspension of Bacillus thuringiensis spores and crystals at a desired concentration was stirred into the starch-oil mixture to form a gelatinous mass. The mixture was allowed to stand for 30 minutes at room temperature to produce a rubbery but non-sticky mass which was processed in a blender with the addition of 25 g of starch powder to produce small particles. After being air dried for 24 hours at room temperature, the particles were sieved into various mesh sizes. This process was applied in order to avoid the reduction of the activity of biocide due to heat or high temperature. However, this process is cumbersome and cannot be performed as a continuous process.
Another disadvantage of the conventional biocides is that most biocides can be easily destroyed upon exposure to sunlight. The ultraviolet rays of the sunlight is specifically harmful to biocides. Thus biocides must be applied frequently and in large quantities in order to supplement the loss due to degradation and thus to effectively kill pests. Since large amounts of biocides, i.e., much larger than the optimum required of biocides, are required to achieve the desired biocidal activity, the conventional method for the application of biocides is not economical; it also can cause health and environmental concerns.
Several researchers have studied the use of anti-ultraviolet agent in order to protect biocides against ultraviolet degradation. R. L. Dunkle et al. discloses the application of 4-aminoazobenzene as an anti-ultraviolet agent in Environmental Entomology (Vol. 17, 120-126, 1988). With their formulation, after the biocide is exposed to ultraviolet rays for 24 hours, the mortality of pests is only 13-63% on the seventh day. In U.S. Pat. No. 3,541,203, M. V. Ogle et al. disclose a method which employs carbon black and metal powder as a protective agent in the biocidal formulation. The mortality of pests reaches the maximum on the fifth day. However, in their tests, they did not expose their biocidal formulation to ultraviolet ray; therefore, it cannot be said that their protective agents are effective as anti-ultraviolet agent. In U.S. Pat. No. 4,918,586, H. A. Bohm et al. disclose a method which employs benzophenone, para-aminobenzoic acid, benzyl, methyl orange, methyl green, malachite green, brilliant green, methyl blue, FDC green, FDC red and acridine yellow as anti-ultraviolet agents. However, with their formulations, the mortality of pest was tested to be in the range of 30.7% and 71.43%.